This invention relates to camera support equipment and tracks for use with camera dollies camera cranes.
Camera dollies are heavy wheeled platforms that hold movie cameras and allow for controlled movement of a movie camera during filming of movies, television shows and other productions. Camera cranes also provide smooth movements of the camera, but provide extended reach of the camera. Camera cranes are usually heavier than camera dollies because they require counterweights and ballast to offset the weight of the camera equipment on the extended end of the cantilever arm of the crane. Camera dollies and cranes generally include mechanisms for controlled lifting and/or panning of the movie camera, wheels and steering systems for movement about a set, and a platform for a cameraman to stand on while the camera dolly is moved about the set by a grip. Many camera dollies have wheel systems that will engage a track of one form or another, so that the dollies may be rolled about a set on a track which has been set down to establish a smooth path for the intended movement of the dolly. The track may be laid down anywhere, and may be used to provide level or smooth dolly pathways in indoor studios and outdoor sets such as parking lots, unleveled fields, beaches, streets, hillsides and mountain sides. The inventions described below are aimed at improved tracks for use with a number of standard wheel systems, and the following background sets forth a description of the standard wheel systems necessary to understand the features of the new dolly track.
Clearly, for a camera dolly to run along a track, the wheels and track must be designed to match each other so that the wheels fit on the track and stay on the track. Currently, there are two competing industry standards for matching wheel and track systems. The first system is a combination of a concave wheel which fits onto a matching convex track. The wheel in this system has a concave groove cut down the center of the running surface of the wheels. This concave groove fits over the radiused top of the track and keeps the wheel from falling off the track. (The outer edges of the wheel provide a flat running surface that is used when the dolly is rolled directly on the floor.) The track may be a simple tube mounted on ties, or it may be made of I-beam rails with radiused upper surfaces. In the I-beam cross section, the major vertical structure is the narrow vertical beam (called a web) which is much narrower than the radiused top. This system is used by such dollies as the Chapman PeeWee dolly, the Panther Pegasus dolly, and several other dollies. One type of radiused track is sold under the name of Precision I-Beam track, and is described in detail in the McKie, Rail and Track, U.S. Pat. No. 4,989,782 (Feb. 5, 1991). The second system uses a flat weight-bearing wheel which runs on a flat-topped square track, in combination with a tensioner wheel which hangs down below the running wheel and presses against the vertical side wall of the square track. The tensioner wheel on each running wheel prevents the dolly from slipping off the flat-topped track, and locks the dolly in place cross-wise on the track. This system has a lot of excess friction between the wheel and the track, making it hard to move on the track. This system is used in dollies manufactured by the J. L. Fisher Co., and the track is also available from the J. L. Fisher Co.
The two types of dolly wheel and track systems are not compatible. Grooved-wheeled dollies cannot be used on flat track, and flat wheeled dollies with tensioner wheels are dangerous when used on radiused track with a centrally arranged vertical wall.
Height and rigidity are important design factors for dolly track. When a camera dolly rides on dolly track, it is several inches higher than when it sits on the floor. For low camera positions, grips must install a lowering plate system. This is time consuming and makes it harder to operate the camera in that position. Thus a shorter track is advantageous in that it limits the need for time consuming installation of lowering plate systems. Height also plays a part in the comfort and natural movement of the actors. Actors occasionally must cross over the track to hit a mark (the position where the director wants him or her to stand). Hidden movement over a 2.5 inch track is unnoticeable on film, while movement over a 4 inch track is very hard to perform with a natural gait, so the fact that the actor is stepping over an off screen obstacle is sometimes apparent.
The current solutions are piecemeal. Regular tube track is just a round pipe that has a sleeper welded on the bottom. The only point of support for the track is at the sleepers, which are provided every few feet along the track. Although tube track may be made with a low profile of about 2.25 inches (6 cm), the problem with this design is that the tube running surface flexes with the weight of the dolly when the dolly is between the sleepers. This creates a porpoise effect, as the dolly passes over peaks and valleys created by the rigid point of track supported by a sleeper, and the flexible portion of the track between the sleepers. This creates an uneven tracking movement and limits the appropriate choices in lens lengths (like driving slowly down the road looking through a pair of binoculars the horizon will be jerking and inconsistent.) Thus stronger, larger track is needed for shots where smooth movement is critical, thus limiting the ability to combine the low shots with smooth movement.
Additionally, tubing is not consistent in tolerance so the mating joints of two pieces of track are very inconsistent and will create a bump at every joint. The tube track system also has problems when you lay it out on a location. The sleepers, which provide the only contact with the ground, are the only place you may level the track. If a sleeper falls in a rut or hole, the track may prove very difficult to level (Box truss and I beam track both have interior sleepers so you can level track anywhere along the bottom surface). The box truss design and the I-beam dolly track are almost 15 to 20 times more rigid than the tube designs, and by being extruded you can guarantee tolerances up to plus or minus a few thousands of a inch, not hundredths like the rolled steel type tube tracks.
The dolly track disclosed below is unique in that it is the only track that can be used with both flat wheeled dollies and cranes with tensioner wheels and grooved wheeled dollies and cranes with tensioner wheels and grooved wheeled dollies and cranes. The new dolly track has a radiused top to accommodate the grooved wheeled dollies, and it has vertical side walls to accommodate the tensioner wheels used with flat wheeled dollies. The track has a high tolerance coupling system and an overall aluminum box truss design made of 6061 aluminum. The track cross section provides such strength that the track may be made in lower heights than other tracks, eliminating or minimizing the limitations on staging imposed by the height of other tracks. The box truss dolly track of 2.5 inches (about 6.5 cm) is almost as rigid as an I-beam track that is 4 inches (10 cm) high.